This application claims priority of Japanese Application No. 2001-114954, filed Apr. 13, 2001, the complete disclosure of which is hereby incorporated by reference.
a) Field of the Invention
The present invention relates to a motor to which a feed screw is formed in a rotation shaft extending out of a motor case and a method of manufacturing the same.
b) Description of the Related Art
Generally, in types of devices such as a head mechanism used for a floppy disk driving device (FDD) or a driving device (ODD) for an optical recording reproduction disc such as CD, DVD or an optical lens driving device of a camera and the like, structure that forms a feed screw (a lead screw) as a rotating shaft of a motor has been broadly adopted.
Such a motor shown in FIG. 4, for example, shows a rotating shaft 2 which is provided so as to extend from the inside of motor case 1 to the outside of the case.
A feed screw (a lead screw) 3 is manufactured (worked) and formed by a ball-race process or by forming in a rolling process in a portion extending out of the motor case of rotating shaft 2.
A moving body is engaged threadedly in feed screw 3. The moving body such as the head or the optical lens described above moves back and forth on feed screw 3.
Furthermore, in general, the rotating shaft 2 is supported rotatably by appropriate bearing member 4 at a boundary portion which is arranged between an internal portion of the motor case and a portion extending out of the motor case.
On the other hand, when feed screw (a lead screw) 3 is formed by forming of a rolling process on a blank of rotating shaft 2, the blank is pressurized by an appropriate rolling tool.
That is, shown in FIG. 5, for example, a wall is built up from both side portions of the part on which screw thread 3a is formed so that the wall comes to screw thread 3a. 
A groove-shaped screw trough 3b is formed in both side portions of screw thread 3a, too.
In the time immediately after the above forming of the rolling process, shown with oblique line in FIG. 5, groove-shaped concavity 3d is formed in the center portion of building up portion 3c of screw thread 3a. 
Further, conventionally, building up portion 3c, including the concavity 3d, is removed by center-less polish.
In addition, after having carried out such center-less polish, a working burr occurs on screw thread 3a. 
After working, deburring is carried out by a process such as a barrel treatment or a buff treatment.
However, as described above, in the motor having feed screw 3 formed in the rotating shaft, it is difficult to maintain lubricity of feed screw 3 and it is a problem that an external scattering of lubricant occurs.
Furthermore, as mentioned above, center-less polish and deburring process after forming of the rolling process comparatively took time.
Accordingly, each process described above is one of the causes of productivity degradation.
In addition, when carrying out these processes, respectively, there is a possibility of a streak and a nick (gouge) occurring in a screw portion so that there is a concern and fear that quality may be decreased.
Thus, a primary aim of the present invention is to improve lubricity of a feed screw by a simple structure and also to offer a motor which can improve both the productivity and quality of a feed screw and to a method of manufacturing the same.
According to the invention, a motor comprises a motor case and a rotating shaft for the motor having a portion within the motor case and a portion extending outside of the motor case. A feed screw is formed on the extending portion of the rotating shaft. The feed screw threadedly engages with a moving body which moves back and forth along an axial direction of the rotating shaft. It is also provided with a concavity to store lubricating oil at the top of a screw thread of the feed screw so that lubricating oil can be stored in the concavity.
Thus, lubricity is well maintained over a long time and lubricating oil which scatters by centrifugal force outside is held with the concavity. As a result, external scattering is well prevented.
Further, according to the invention, it is provided that bearing materials are arranged at opposite end portions between a bottom portion of an end side of an internal portion of the motor case of the rotating shaft and a top portion of the portion extending out of the motor case. The bearing materials support the rotating shaft. Further, sphere members are arranged to protrude from the end portions of the rotating shaft in an axial direction. The sphere members are rotatably supported on the bearing materials.
Thus, a bearing material is not attached at a boundary portion of the rotating shaft which is arranged between the internal portion of the motor case and the portion extending out of the motor case.
The feed screw is formed on the boundary portion of the rotating shaft without waste so that an active length of the feed screw is expanded.
Furthermore, it is possible to shorten the overall length of the rotating shaft in an axial direction, and the boundary portion of the rotating shaft does not need a bearing surface to which the bearing material is attached for polishing of the bearing surface. That is, a center-less polishing process and a deburring process after forming of the rolling process and the like is not needed. As a result, productivity and quality are improved.
Furthermore, according to the invention, a method is provided for forming a feed screw on a portion extending out of the motor case of a rotating shaft which is provided so as to extend from inside of the motor case to outside of the case by forming of the rolling process; the feed screw having a top of a screw thread and the screw thread top having a concavity to store lubricating oil.
Accordingly, lubricity of the feed screw is well maintained over a long time and after forming of the rolling process of the top of the screw thread, center-less polish of the top of the screw thread is not carried out so that deburring process after center-less polish is not needed. Thus, productivity and quality are improved simultaneously.
Furthermore, according to the invention, a method is provided where the bearing materials, respectively, which support the rotating shaft, are arranged at opposite end portions between a bottom portion of an end side of an internal portion of the motor case of the rotating shaft and the top portion of the portion extending out of the motor case; and sphere members, respectively, are provided which are arranged to protrude from the end portions of the rotating shaft in an axial direction. The sphere members are supported rotatably by the bearing materials.
Accordingly, the motor is manufactured such that a bearing material is not attached at a boundary portion of the rotating shaft which is arranged between the internal portion of the motor case and the extending portion out of the motor case.
There is a possibility of using the boundary portion of the rotating shaft as an area of shifted wrinkles which occur by forming of the rolling process so that a feed screw is formed without waste and an active length of the feed screw is expanded. It is possible to shorten an overall length in an axial direction of the rotating shaft.
The boundary portion of the rotating shaft does not need a bearing surface to which a bearing material is attached for polishing of the bearing surface. That is, the center-less polishing process and the deburring process after forming of the rolling process and the like is not needed. As a result, productivity and quality are improved.
Preferred embodiments of the present invention will hereinafter be described in detail with reference to the attached drawings.